This invention relates to cathode ray tubes (CRTs) of the type having an implosion band, and more particularly relates to such tubes having an implosion band with means for attachment of components such as degaussing coils, and also relates to a method for producing such a band.
Color CRTs for color television and allied display applications basically comprise an evacuated glass envelope including a face panel portion and a funnel portion, a phosphor screen on the interior surface of the face panel, and an electron gun in the neck of the funnel for generating electron beams to excite the phosphor elements on the screen.
It is customary to place the face panel in mechanical compression by strapping a steel band around the side wall or skirt of the panel, so that in the unlikely event of an implosion, the glass fragments will tend to be contained within the tube area or only a short distance away from it. Such bands are known as implosion bands. A particular type of implosion band is the so-called tension band, which is applied by wrapping it around the panel skirt, overlapping the ends and fastening these overlapped ends with a tensioning device.
A newer type of implosion band which is coming into increasing use is the shrink band. This is a steel band which is joined end-to-end and pre-formed prior to placement on the CRT panel. The formed band is heated to cause thermal expansion sufficient to allow placement of the band around the panel skirt, and then allowed to cool and "shrink" onto the panel, thereby placing the band in tension and the panel in compression.
Implosion bands often perform an added function of supporting tube mounting brackets, used to mount the tube in a display cabinet. In addition, such bands often serve to secure other CRT parts or components, such as clips for holding degaussing coils. In a typical arrangement, the band has sufficient width so that a portion extends rearward over the seal between the faceplate and the funnel portion of the envelope, to form its own skirt portion spaced a small distance above the inwardly curving surface of the funnel. The width and placement of the band are chosen so that sufficient clearance is provided between the band skirt and the funnel to allow attachment of clips to the band through openings formed in the band skirt by a separate punching operation. Additional clearance may be provided by forming the band skirt with a slight outward offset from the body of the band. See in this regard Toshiba Japanese patent applications 55-111048 and 55-96541.
In addition to the extra band width required to form the skirt, and the separate punching operation needed to form the openings in the skirt, the presence of the skirt tends to interfere both with the mounting of components such as degaussing coils on the tube funnel, and with the mounting of the tube in the television cabinet.